HyperTextTransferProtocol (HTTP), e.g., RFC 2616 HTTP/1.1 June 1998, makes a desirable communication protocol because it is well understood, well documented, proven robust, and it is flourishing. A communication method operating under HTTP finds compatibility with existing standards such as the following HTTP extensions: Simple Object Access Protocol (SOAP), eXtensible Markup Language (XML), Distributed Authoring and Versioning (DAV), Web Services Description Language (WSDL), Universal Description Discovery & Integration (UDDI), as well as security standards such as Secure HTTP (S-HTTP), and other standards likely to emerge to extend existing web client browsers and servers providing HTTP communication. These extensions to HTTP are confined by and limited to the asymmetries of HTTP as discussed more fully hereafter. HTTP protocol and its extensions will likely enjoy continued success by sheer volume of use and momentum of use as the dominant method of communication on, for example, the Internet.
HTTP transactions, or sessions, consist of a series of requests and responses. A session originates with a client request and concludes with a server response. A variety of additional rules dictate the sequence of transactional interchange occurring in an HTTP session. Overall, however, HTTP sessions follow a client request and server response transaction scenario. A session can terminate following completion of an HTTP transaction sequence, or after a time-out period in the event of no server response. A KEEP ALIVE request from the client may increase a given session timeout period by requesting that server not terminate the connection. However, once a transaction is completed the server is not obligated to maintain the connection.
By nature, an HTTP session is transactional, e.g., exists for, and substantially only during, a given transaction scenario. Furthermore, the relationship is highly asymmetrical, e.g., the client dictates the time of initiating each session. The server has no such ability.
The HTTP protocol has been implemented generally over the TCP/IP network protocol. As such, TCP/IP provides an underlying transport connection between HTTP client and server including network node addressing and data packet exchange. The TCP/IP network protocol has proven itself an enormous success as applied not only in a global network application, e.g., the Internet, but also across a wide spectrum of private networks. TCP/IP constitutes by sheer volume of use and momentum a virtually universal mode of interaction between users and computing devices operated by such users.
The TCP/IP network address space is generally partitioned into a single public address space and numerous private address spaces connected to this public address space by means of Network Address Translation or proxy servers. A typical TCP/IP connection traverses not only public/private address space boundaries but multiple organizational jurisdictions, encountering different equipment configurations, bandwidth management policies and security policies implemented in hardware and software, all of which must be successfully negotiated at the TCP/IP layer for the overlaying HTTP or other protocol to be successful in establishing and maintaining end-to-end communication.
Because of the nature of TCP/IP networks described above, there is a fundamental problem to be solved for applications that desire to take advantage of HTTP and its extensions to negotiate the labyrinth of network jurisdictions and permissions, while treating all network nodes as functional peers. Under HTTP, participating network nodes play asymmetric roles where one, the client, initiates a conversation by making a request and the other, the server, responds. Common understanding of the HTTP protocol suggests a public node, e.g., having a published or known, routable network address, is always the server, while a private node, e.g., having a generally unknown and/or unpredictably dynamic local network address, is generally the client. The client polls the server with requests and the server responds. The two nodes do not act as functional peers. The server node cannot initiate a spontaneous request and a client node cannot receive a spontaneous request.
Thus, as the Internet has developed, certain roles have evolved rigidly and asymmetrically with respect to HTTP communication. Certain computing devices assume exclusively the role of “server” and receive requests for information, e.g., documents maintained under the HTTP protocol, and other devices assume exclusively the role of “client” and request such documents. Under such evolution, therefore, HTTP communication has evolved in an asymmetrical fashion with respect to the underlying TCP/IP network, which is generally symmetrical. More particularly, clients request information from servers and servers provide, when possible, the requested information. A device assumes a “server” role and does not initiate communications, but rather stands ready and accessible to others sending requests thereto. A server does not initiate HTTP communication with a client. For this reason, HTTP communication between a server and a client is limited to those communications initiated by a client, i.e., initiated by a request originating from a client and directed toward a particular server.
This strong correlation of the role of devices with the asymmetrical HTTP model has also become fixed in network hardware, software and corporate network security policies. When two or more nodes do not share a common Internet address space, they encounter Network Address Translation, or proxying, both of which typically depend upon the private address device being the client and the public address device being the server. Security restrictions, in the form of firewalls, deployed at one or more routers operating between nodes, typically enforce similar asymmetries, rendering useful symmetrical bi-directional HTTP communication unavailable.
Thus, the Internet is built around the asymmetrical private client-public server description of HTTP. In practice heretofore, a peer-based model of communicating on the Internet was likely blocked from using HTTP and its extension and likely blocked from taking advantage of all the benefits surrounding it.
Asymmetrical HTTP communication in both directions has been addressed, but it is inefficient and unsuitable for peer-based networks. For example, a “polling” method of HTTP communication has been proposed where a client intermittently asks or polls a server, the client inquiring whether or not the server needs to communicate with the client. Under this arrangement, the server does not initiate communications, but rather waits for a request from a client. This request opens communications and permits the server to provide any pending communication to the client. For example, HTTP GET and PUT commands facilitating bi-directional file exchange between the client and server can then commence.
Polling for information on the server undesirably wastes network bandwidth. Most requests will evoke a null response. Given a peer-based network topology providing many-to-many peer connections, and multiplying the number of nodes by the number of connections by the number of different types of requests likely to be generated by each peer, a polling solution does not scale into a useable model. An overwhelming amount of network traffic consists of request-response pairs characterized by: “Now? No!”. More importantly, because server nodes cannot initiate connections with client nodes under HTTP, a peer-based network based upon HTTP would require that all client nodes always poll all server nodes to maintain complete network connectivity, incurring the worst-case bandwidth penalty described above.
Thus, as server and client roles evolved and the use of HTTP communication therebetween grew rapidly, symmetrical communication between entities operating on, for example, the Internet has been limited. It would be desirable, therefore, to provide improved symmetrical communication compatible with the HTTP protocol. The subject matter of the present invention provides such symmetrical communication.